Tone synthesizers in which an aduio tone rich in harmonics is passed through a sliding formant filter to produce a time-varying tonal effect by altering the higher frequency components of the signal are well known. In analog systems, the sliding formant filter may be a high or low pass filter in which the cutoff frequency may be varied with time to change the harmonic content of the output of the filter. In digital systems, the equivalent effect of a sliding formant filter is achieved by scaling the harmonic coefficients before they are used in a computational alogorithm to obtain amplitude values determining points of the musical waveshape of the tone being generated. Digital systems having the equivalent effect of a sliding formant are described, for example, in U.S. Pat. No. 3,956,960 entitled "Formant Filtering in a Computer Organ" and in copending application Ser. No. 603,776, filed Aug. 11, 1975, entitled "Polyphonic Tone Synthesizer", now issued as U.S. Pat. No. 4,085,644. Scaling of the coefficients, however, requires the use of a digital multiplier, which is a relatively expensive circuit element.